2007 Suburban 4x4 (obviously), ~167,000.Went to kick on 4WD yesterday and couldn't get it to engage. When I spin the dial to 4HI, 4LO, or N it just flashes for ~30 secs and then goes back to 2WD solid light. If I go to Auto in flashes and locks into Auto, but I'm not sure that actually engages the transfer case until it senses slip. When I spin the dial I don't hear anything trying to engage, but not sure how loud it is, going to climb under the truck today to really put my ear to it. Doing quick searches it sounds like bad fuses, old oil in transfer case or something electrical. Anyway I can start narrowing it down? I checked the fuses and didn't see any blown, but also couldn't ID which one specifically would be for engaging the front axle. Oil has ~50k-60k on it so I doubt it's the culprit, car is a daily driver not on heavy tow duty.Any help pointing me in the right direction would be great.Thanks.-Svence